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A Little More Advanced Biotechnology Tools
Better Plasmids
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Engineered plasmids Building custom plasmids restriction enzyme sites
antibiotic resistance genes as a selectable marker EcoRI BamHI HindIII restriction sites Selectable marker antibiotic resistance gene on plasmid ampicillin resistance selecting for successful transformation successful uptake of recombinant plasmid How do we know what’s the right combination of genes on a plasmid? Trail and error research work. selectable markers high copy rate convenient restriction sites There are companies that still develop plasmids, patent them & sell them. Biotech companies (ex. New England BioLabs) plasmid ori amp resistance
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Selection for plasmid uptake
Antibiotic becomes a selecting agent only bacteria with the plasmid will grow on antibiotic (ampicillin) plate only transformed bacteria grow all bacteria grow a a a a a a a a a a a a a a a a a LB plate LB/amp plate cloning
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Need to screen plasmids
Need to make sure bacteria have recombinant plasmid restriction sites recombinant plasmid amp resistance broken LacZ gene inserted gene of interest EcoRI all in LacZ gene BamHI HindIII LacZ gene lactose blue color lactose white color X plasmid amp resistance origin of replication
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Screening for recombinant plasmid
Bacteria take up plasmid Functional LacZ gene Bacteria make blue color Bacteria take up recombinant plasmid Non-functional LacZ gene Bacteria stay white color Which colonies do we want?
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Finding your “Gene of Interest”
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Finding your gene of interest
DNA hybridization find sequence of DNA using a labeled probe short, single stranded DNA molecule complementary to part of gene of interest labeled with radioactive P32 or fluorescent dye heat treat DNA in gel unwinds (denatures) strands wash gel with probe probe hybridizes with denatured DNA G A T C labeled probe genomic DNA C T A G T C A T C
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Southern blotting restriction digest gel electrophoresis
blot DNA off of gel onto filter paper expose filter paper to X-ray film wash filter with labeled probe
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Southern blot IDing one gene Southern blot illustration
Edwin Southern Southern blotting Northern blot: RNA on filter & DNA probe measures gene expression because grabbing mRNA from cell -- only expressed genes Western blot: protein on filter labeled directly gel of genomic DNA Southern blot IDing one gene Southern blot illustration
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DNA libraries Cut up all of nuclear DNA from many cells of an organism
restriction enzyme Clone all fragments into many plasmids at same time “shotgun” cloning Create a stored collection of DNA fragments petri dish has a collection of all DNA fragments from the organism
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Making a DNA library 2 1 engineered plasmid with selectable marker & screening system all DNA from many cells of an organism is cut with restriction enzymes gene of interest 3 all DNA fragments inserted into many plasmids human genome = 3 billion bases fragments are cut to ~5000 bases therefore ~ 600,000 fragments per cell. But you have to use many cells to make sure you have a complete set in the library, so… you may have millions of cells that you extracted the DNA from, so… you would need millions of colonies, so the human genome cloned into bacteria would be a walk-in freezer full of petri dishes. 4 clone plasmids into bacteria
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But how do we find colony with our gene of interest in it?
DNA library recombinant plasmids inserted into bacteria gene of interest human genome = 3 billion bases fragments are cut to ~5000 bases therefore ~ 600,000 fragments per cell. But you have to use many cells to make sure you have a complete set in the library, so… you may have millions of cells that you extracted the DNA from, so… you would need millions of colonies, so the human genome cloned into bacteria would be a walk-in freezer full of petri dishes. ? DNA Library plate of bacterial colonies storing & copying all genes from an organism (ex. human)
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Find your gene in DNA library
Locate Gene of Interest to find your gene you need some of gene’s sequence if you know sequence of protein… can “guess” part of DNA sequence “back translate” protein to DNA if you have sequence of similar gene from another organism… use part of this sequence Complementation if you have a mutant that lacks YFG, you can transform bacteria with plasmids from the library until one “cures” (complements) the mutation ? Which bacterial colony has our gene? Like a needle in a haystack!
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Colony Blots 4 1 3 2 Locate expose film Cloning
locate colony on plate from film 1 Cloning - plate with bacterial colonies carrying recombinant plasmids plate plate + filter film 3 2 Replicate plate press filter paper onto plate to take sample of cells from every colony Hybridization - heat filter paper to denature DNA - wash filter paper with radioactive probe which will only attach to gene of interest filter
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Problems… Human Genome library Clean up the junk! introns
are there only genes in there? nope! a lot of junk! human genomic library has more “junk” than genes in it Clean up the junk! if you want to clone a human gene into bacteria, you can’t have… introns
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How do you clean up the junk?
Don’t start with DNA… Use mRNA copy of the gene without the junk! But in the end, you need DNA to clone into plasmid… How do you go from RNA DNA? reverse transcriptase from RNA viruses retroviruses reverse transcriptase
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cDNA (copy DNA) libraries
Collection of only the coding sequences of expressed genes extract mRNA from cells reverse transcriptase RNA DNA from retroviruses clone into plasmid Applications need edited DNA for expression in bacteria human insulin Could you imagine how much that first insulin clone was worth to Genentech? One little piece of DNA in a plasmid worth billions! It put them on the map & built a multi-billion dollar biotech company.
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reverse transcriptase
Where do we go next…. DNA RNA protein trait When a gene is turned on, it creates a trait want to know what gene is being expressed extract mRNA from cells mRNA = active genes How do you match mRNA back to DNA in cells??? reverse transcriptase
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Microarrays slide with spots of DNA each spot = 1 gene
Create a slide with a sample of each gene from the organism each spot is one gene Convert mRNA labeled cDNA mRNA cDNA mRNA from cells reverse transcriptase
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Microarrays Labeled cDNA hybridizes with DNA on slide
slide with spots of DNA each spot = 1 gene Microarrays Labeled cDNA hybridizes with DNA on slide each yellow spot = gene matched to mRNA each yellow spot = expressed gene cDNA matched to genomic DNA mRNA cDNA Developed by Pat Brown at Stanford in late 1980s Realized quickly he needed an automated system: robot spotter Designed spotter & put plans on Internet for benefit of scientific community.
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Application of Microarrays “DNA Chip”
2-color fluorescent tagging Comparing treatments or conditions = Measuring change in gene expression sick vs. healthy; cancer vs. normal cells before vs. after treatment with drug different stages in development Color coding: label each condition with different color red = gene expression in one sample green = gene expression in other sample yellow = gene expression in both samples black = no or low expression in both It’s all about comparisons! Powerful research tool.
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EcoRI BamHI HindIII restriction sites plasmid ori amp resistance
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